The invention relates to V-belts, but more particularly, the invention relates to V-block belts.
V-block belts are extensively used as variable speed belts because their construction allows a low thickness to width ratio to accommodate desirable speed ratio changes in variable speed drives. Such belts are usually constructed with a flat band type load-carrying member that establishes an equatorial plane about which bending takes place. V-blocks are longitudinally spaced and attached to the load carrying member. Such belts usually fall within two categories. In one category of belts, V-blocks surround and slide on a metallic flat band member. The V-blocks are made of a high modulus material that directly contacts conical sides of a pulley without the aid of a polymeric friction wear surface. In such belts, power is transmitted by successive blocks pushing against each other. An example of such a belt appears in U.S. Pat. No. 4,457,742.
Belts in a second category have V-blocks attached directly to a flat band-type load-carrying member. Such belts transmit power by the blocks pulling and tensioning the load-carrying member. One type of belt in this category has V-blocks clamped to the load-carrying member. The blocks may be of leather and extend transversely of a load-carrying member and define a friction wear surface. An example of such a belt is shown in French Pat. No. 573,783. Another belt where the friction wear surface and the transverse portion of the block are of a low modulus material such as leather or rubber is shown in Swiss Pat. No. 256,918. Belts of this type have limited power transmission because the wear-resistant surface and transverse member are made of the same low modulus materials such as leather.
Another type of belt in the second category has V-blocks which each have a high modulus reinforcement such as of metal or plastic that surrounds and supports a load-carrying member. Wear pads made from a polymeric material are attached to the reinforcement at oppositely facing V-sides. Such belts are capable of transmitting much higher power than the previously described belts. An example of a V-block belt having a high modulus reinforcement is shown in U.S. Pat. No. 4,177,687. The belt of the invention is directed to belts of this second type.
The art of the exemplary categories teaches or shows belts with V-blocks that have transversely oriented surface portions that are in contact with each other.
As with all conventional V-belt drives, power is transmitted between a driver pulley and a driven pulley by means of belt tension where T.sub.1 is commonly referred to as the tight side belt tension and T.sub.2 is commonly referred to as belt slack side tension. The difference between T.sub.1 and T.sub.2 (T.sub.1 -T.sub.2) is representative of a force acting at a changing pulley radius for transmitting torque at the driver and driven pulleys. FIGS. 5 and 6 are schematical representations of a V-belt drive with superimposed radial plots of belt tension about a driver 6 and driven 8 pulleys for a speed down condition (FIG. 5) and a speed up condition (FIG. 6). The distribution of belt tension is drastically different between the driver and driven pulleys even though both pulleys are exposed to the same tight side tension T.sub.1 and slack side tension T.sub.2. Belt tension at the driver pulley remains substantially high throughout the total arc of belt contact from the point where the belt enters the pulley to the point where the belt exits the pulley as it is released to the slack side tension. In contrast, belt tension at the driven pulley starts out at the low slack side tension and almost exponentially increases to the tight side tension level where the belt exits. This happens for both the speed down and speed up cases. The maximum tensile and shear loads between the belt and a pulley are imposed just before the belt exits the driven pulley.
A V-block belt undergoes a similar tension change between slack side tension and tight side tension except that each V-block must carry an incremental portion of the increased tension at the driven pulley. The V-block that is just ready to exit the driven pulley may be exposed to higher shear forces in comparison to all of the other V-blocks that are engaged with either pulley. FIG. 7 illustrates the incremental shear forces for successive blocks in comparison to a conventional, continuous belt. The large difference in shear forces between V-blocks does not present a significant problem for the low horsepower belts (i.e., 10 HP or less). However, the large differences in shear loading of the V-blocks and tension loading between V-blocks for high horsepower belts (i.e., 20 HP or more) presents a loading problem between the exiting V-block and pulley, and a load transferring problem between the V-block and the load-carrying member. This invention is directed to improving the power transfer between a V-block belt and a pulley.